In augmentor systems (also known as afterburners) fuel is not used on a continuous basis. However, in order to ensure acceptable response times, it is desirable that fuel be available at the augmentor nozzle when the augmentor is activated. Unfortunately, the temperatures of the augmentor manifold are normally high enough to vaporize stagnant fuel. Thus, stagnent fuel in the augmentor manifold tends to vaporize when the augmentor nozzles are closed. When fuel vaporizes it tends to leave carbon deposits which may block the augmentor nozzles. These carbon deposits are known as coking.
When an augmentor's nozzles are opened and fuel flows, the augmentor is said to be in the "active" mode. When the nozzles are closed, the augmentor is said to be in the "dry" mode. One method of preventing evaporation is to circulate fuel through the augmentor manifold during "dry" periods. Since the circulating fuel does not evaporate, coking does not occur.
It will be recognized that the technique of circulating fuel may be used in any high temperature environment, for example, in combustors, to prevent evaporation and carbon buildup. Thus, for the purpose of the present application, the term fuel disbursement means will be used to describe apparatus such as augmentors and combustors which disburse fuel into a region such as an exhaust nozzle or combustion chamber.
In a fuel flow apparatus in which fuel is continuously circulated through the manifold of a fuel disbursement means, it would be advantageous to provide a means for accurately controlling the flow of fuel to the fuel disbursement means. More particularly, it would be advantageous to provide a fuel disbursement control system designed to account for the continuous circulation of fuel and adjust the valve supplying fuel to the disbursement means to compensate for the continuously circulated fuel.